The present invention relates to a method and apparatus for reproducing the audible sound produced by a heartbeat in order to facilitate the diagnosis of coronary diseases and abnormalities and to aid in teaching such diagnoses.
A heartbeat is a single complete pulsation of the heart, consisting of a complete cardiac contraction-relaxation sequence, and produces an audible sound pattern. Contraction is represented by the first sound S.sub.1, the beginning of relaxation by the second sound S.sub.2. In addition, sounds may take any one of a number of different forms based on the duration and the relationship to S.sub.1 S.sub.2. The audible sound pattern produced by a single heartbeat may be classified as heart sounds, or heart murmurs, or a combination of a heart sound and a heart murmur. A heart murmur is a protracted sound usually over 40 msec which may occur in systole during cardiac contraction or in diastole during cardiac relaxation. A heart sound is a nonprotracted sound and a murmur is a protracted sound. Either a heart sound or a murmur may take one of a number of specific forms. Depending on its specific form, a heart sound may be indicative of a normal, healthy, heart, or an abnormal or diseased heart. A diastolic murmur is usually abnormal. Diastolic murmurs are heard between the second and first sounds.
Hereinafter, the term "heartbeat" will be understood to refer to either a heart sound, or a murmur, or a combination thereof; the sounds produced by one heartbeat will be referred to as an audible sound pattern, or sound pattern; and sounds produced by a plurality of successive heartbeats will be referred to as audible sound patterns, or sound patterns.
Interpretation of the audible sound pattern produced by a heartbeat, or more generally the audible sound patterns produced by a succession of heartbeats, is known as auscultation and represents one of the oldest, and most effective, techniques used in the practice of medicine. A skilled and experienced physician can obtain critical information about the condition of a patient's heart from proper interpretation of such audible sound patterns.
However, auscultation is inherently a demanding art and is rendered more difficult by the fact that an irregularity and/or the relatively high repetition rate of heartbeats interferes with the mental processes involved in such interpretation.
Specifically, heartbeats produce repetitive audible sound patterns which are substantially identical from one heartbeat to the next. Because of the rate at which successive heartbeats normally recur, it has been found that after a physician has heard one heartbeat, and is attempting to interpret it, the next heartbeat occurs and interferes with the interpretation process.
It has been proposed to facilitate diagnosis by recording the audible sound patterns produced by a succession of heartbeats in auscultable grouped units (see Det) and then playing back the recording at a reduced rate, or speed, to facilitate interpreting the grouped sounds. Normally, this procedure has a significant drawback in that it reduces the frequency components of all of the recorded heartbeat, with the result that the heartbeats which are reproduced for diagnosis differ significantly from the actual heartbeats which physicians have been trained to interpret (defined as auscultable sounds).